Pumps, including liquid pumps, have been well known in the industry for years. Generally described, such pumps typically include a mechanical input such as an input shaft, which accepts energy and transfer it to fluid within the pump to cause the fluid to move through the pump from its inlet to its outlet port and further on to a remote location.
Many types of fluid pumps have been developed throughout the industry. Such pumps include rotary pumps (such as lobe, external/internal gear, progressing cavity, etc.) piston pumps, and centrifugal pumps.
As noted above, pumps typically have an inlet and an outlet port, as well as a mechanical power input. As can be understood, there are multiple locations and orientations where such ports and power inputs can be placed during the design of such pumps. As engineering preferences tend to carry by designer, this gives rise to a tendency for different pump manufacturers to develop their own differing designs. This can provide difficulties to end users, not the least being difficulties in replacing pumps of manufacturers which have discontinued the pump model or have gone out of business.
The above-discussed disadvantages have given rise the use of various standards, including ANSI standards. To conform to such standards, manufacturers must provide products which conform to certain dimensional or structural standards. For example, an ANSI standard for a 1 HP electrical motor might specify the output shaft size and length as well as the height of the shaft relative to the lower surface of mounting feet. This would allow and engineer or like designer to design a system including a 1 HP electrical motor with such dimensions in mind without regard to which manufacturer will be used to supply the motor. The purpose of the ANSI standard pump is to ensure dimensional interchangeability of the pump, for ease of replacement, spare parts inventory, and standardization of maintenance techniques. ANSI specifications can include inlet flow location, outlet flow location, rear foot location, drive shaft location, front feet location drive shaft diameter, port sizes and foot hole sizes.
In the fluid pump industry, the ANSI specification has traditionally been applied to centrifugal pumps, allowing easy retrofitting of these dimensionally interchangeable pumps from one pump manufacturer to another. However, rotary pumps have traditionally been produced without the compliance to ANSI dimensional standards, even though they are used for a wide variety applications.
Although centrifugal pumps are presently afforded the advantage of an ANSI specification, they nevertheless have their own disadvantages. For example, centrifugal pumps only can pump in one direction; to allow for bidirectional pumping two centrifugal pumps must be used--one for loading and another for unloading, which necessitates the use of complex piping, valving, and auxiliaries. For centrifugal pumps, a change in fluid properties can also result in a definite change in performance. Centrifugal pumps also cannot provide an effective metering function. Centrifugal pumps are likewise plagued by problems relating to low flow instability, susceptibility to inlet piping, low efficiency, high radial thrust, leading to low MTBF and premature failures of seals, bearings and other components.
Aside from the need of standards, in the past several years, the issues of pump reliability, maintenance, dependability and cost have found a renewed focus. With the industry drive toward inventory reduction and simplification of operation, it is becoming increasingly important for pump manufacturers to supply pumps having ability to fit as wide range of applications as possible, without compromising reliability and dependability.
Therefore there is a need in the industry for a rotary pump which conforms to ANSI standards yet is reversible, is efficient, is self priming, has low flow stability, low radial thrust characteristics, handles viscous fluids well, and can pump fluid within a high range of pressure values.